Hydraulic pump or motor device pistons



June 8, 1965 c. J. RICKETTS 3, 4

HYDRAULIC PUMP OR MOTOR DEVICE PISTQNS Filed Aug. 19, 1963 2 Sheets-Sheet 1 INVENTOR.

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June 8, 1965 c. J. RICKETTS HYDRAULIC PUMP OR MOTOR DEVICE PISTONS Filed Aug. 19, 1963 2 Sheets-Sheet 2 United States Patent 3,187,644 HYDRAULEC PUMP 0R MOTOR DEVICE llSTONS Charles J. Ricketts, Rockford, Ill., assignor to Sundstrand Corporation, a corporation of lllinois Filed Aug. 19, 1963, Scr. No. 302,964 20 Claims. (Cl. 92-248) This invention relates in general to fluid pressure translating devices of the reciprocating type, and more particularly to a new and improved piston construction particularly adapted for use in hydraulic pumps or motors.

In axial as well as radial piston types of pumps or motors, as the operating speed of the unit increases, the inertia forces on the pistons increase in proportion to the square of the speed. Thus in a high speed and high pressure hydraulic pump or motor the pistons and cylinders are subjected to high stresses and high rubbing velocities. In order to reduce the effects of-these high inertia forces, it is desirable that the piston be made of a wear reistant material capable of withstanding high stresses, and it is necessary that the piston be made as light as possible. In order to reduce the weight of the piston, it is conventional to remove the center section of the piston by means of a drilled or otherwise formed cavity.

In the use of hollowed piston constructions, it has been found that adverse side effects have been introduced into the system due mainly to the compressibility of the oil which fills the piston cavity. The compressibility of the fluid has a marked effect upon the over-all efiiciency of the unit, and also produces cavitation, erosion, noise and undesirable moments on the swash plate mechanism when used in an axial piston type pump or motor. The general purpose of the present invention is, therefore, to provide a light weight piston device for use in a hydraulic pump or motor which obviates the disadvantages noted above. To achieve this, the present invention provides for incorporating in the cavity a filler body formed of an inert lightweight material having a sufiiciently high bulk modulus so as to negate the effects of compressibility.

An object of the invention is to provide an improved piston construction of the character described.

Another object of the invention is to provide an improved piston construction which is eflicient in operation, relatively inexpensive to manufacture, and relatively simple in construction.

A further object of the investion is to provide an improved tiller body for use in a hollowed piston. V

a A still further object of the invention is to provide a plastic filler body for a hollowed piston which can be molded into the piston cavity.

Still another object of the invention is to provide a piston construction as set forth in the preceding paragraph with improved means for retaining the filler body against movement within the piston cavity.

And another object of the invention is to provide an improved piston construction as set forth in the preceding paragraph with means for conveying fluid through the piston for purposes of hydrostatically balancing piston shoes, or to provide lubrication at the opposite end of the piston.

These and other objects will become readily apparent from the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is a longitudinal section of a hydraulic fluidtranslating device incorporating one embodiment of the present invention;

FIG. 2 is a central sectional view on an enlarged scale of the improved piston construction used in connection with the device illustrated in FIG. 1;

FIG. 3 is a left hand end view of the structure shown in FIG. 2;

FIG. 4 is a fragmentary view of a portion of the filler body on a greatly enlarged scale;

FIG. 5 is a longitudinal sectional view of another form of hydraulic fluid translating device incorporating a second embodiment of the present invention;

FIG. 6 is a side view of a piston used in connection with the apparatus illustrated in FIG. 5;

FIG. 7 is an end View, partially in section, of still another form of hydraulic fluid translating device incorporating a further embodiment of the present invention; and

FIG. 8 is a central sectional view on an enlarged scale of the piston used in connection with the apparatus illustrated in FIG. 7. v

While this invention is susceptible to embodiment in many different forms, there is shown in the drawings and will herein be described in detail several embodiments of the invention and modification thereof, with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiments illustrated. The scope of the invention will be pointed out in the appended claims.

Referring now to the drawings, and particularly to FIG. 1, an axial piston type of hydraulic fluid translating device is shown which is similar to that disclosed in the copending application of Hann et al., Serial No. 212,964, filed July 27, 1962, having the same assignee as the present invention. The axial piston pump or motor includes a housing indicated generally at 10 having an end plate 11 removably secured thereto by suitable screw or bolt means, not shown. A drive shaft 12 is rotatably supported at opposed ends of housing It) by suitable bearings 15 and 16, which also secure drive shaft 12 against axial movement. Shaft 12 is drivingly connected, as by splines 13, to a cylinder block 14 for rotation of cylinder block 14 and drive shaft 12 together.

Cylinder block 14 includes pistons, two of which are shown at 20, reciprocally mounted within bores or cylinders 23 in cylinder block 14. Cylinders 23 are provided with bearings, inserts or bushings 25 formed of a suitable material, such as bronze or the like, within which the pistons reciprocate. Although only two pistons are shown in.

FIG. 1, it is to be understood that cylinder block 14 includes an annular plurality of axially disposed cylinders within the cylinder block, each cylinder having an inner end of a piston reciprocating therein. Cylinder block 14 is usually, though not necessarily, formed of a suitable steel or steel alloy.

. A cam plate 31 is mounted within housing 10 at one end of cylinder block 14 for pivotal movement about an axis transverse to and intersecting the axis of the drive shaft. The pivotal mounting of cam plate 31 isprovided by trunnions secured to housing It) and indicated generally at 28 and 29. The cam plate is adapted to be pivoted about its axis at an incline in either direction with respect to a neutral central position for adjustment of displacement of the pistons within the cylinder block cylinders; Conventional means may be provided for effecting pivotal movement of cam plate 31 as described in the aforementioned patent application. V

Bearing shoes 34 on the spherical ends 21 of pistons 20 engage a thrust bearing member 32 that is rotatably supported on cam plate 31. A hold-down member, such as ring 35, holds bearing shoes 34 on thrust plate 32. A spherical collar 36 is splined to shaft 12, and engages a spherical seat in hold-down ring 35 to urge hold-down ring 35 toward the bearing surface of thrust plate 32, and

thus urge the bearing shoes 34 against the bearing surface. A plurality of angularly spaced springs, one visible at 37, grounded upon shaft 12, as by seating against collar 38, urge spherical collar 36 toward bearing plate 35. A second spring means, in the form of a coil spring 43 surrounding shaft 12 and grounded thereon against collar 38, bears against a suitable annular ring 44 to urge the cylinder block 14 against a hardened bearing plate 51 which is pinned to the cylinder block and which is urged against a port plate 52. Port plate 52 is provided with suitables inlet and outlet openings as at 53, for conveying fluid to and from cylinder ports 23' as cylinder block 14 and plate 51 rotate together.

As is best seen in FIG. 2 and FIG. 3, piston includes an axially elongate body 200 which is generally cylindrically shaped, and which includes a portion of reduced diameter-201 adjacent the forward end thereof which blends into spherical end 21. Piston 20 is preferably formed of a wear resistant material that is capable of withstanding high stresses, such as a heat treated steel or steel alloy. In order to reduce the weight of piston 20, an axially elongate generally cylindrical cavity 202 is formed generally centrally therein, and extends substantially the-entire length of body 200. An axially extending centrally disposed opening 203 is formed in the forward end of piston 20, the purpose of which will hereinafter become apparent.

In order to prevent adverse compressibility effects due to the presence of oil in cavity 202, a filler body 204 is provided in the cavity. Filler body 204 is preferably an inert, light-weight material of suificiently high bulk modulus as to avoid significant compression by fluid. Lightweight metallic materials such as aluminum or magnesium, and alloys thereof, are suitable for this purpose, however, because of their relatively high cost, and the difficulty of anchoring them within the piston, they have in general proved to be less desirable than some other materials. Accordingly, the present invention proposes to form the filler body 2040f a suitable plastic material, such as thermosetting'asbestos filled phenolic resin, a satisfactory form of which is commercially available from the Durez Plastics Division, Hooker Electrochemical Company, 500 Walch Road, North Tonawanda, New York, as Durez No. 18975 or No. 22410. Such a material may be conveniently transfer molded or compression molded .into the cavity 202.

Other materials may be poured or injection molded, if desired. The cavity 202 in piston 20 may be formed by drilling, or if desired, the piston 20 may be forged with the cavity 202 being formed in the forging operation. A central axially extending hole 205 is formed 'in filler body 204, and is positioned in alignment with the hole 203 in the forward end .of the piston 20, to allow fluid to flow through the piston from cylinder 23 to provide lubrication to the forward end of 'the piston, and to hydrostatically balance piston shoes 34. Passage 205 may be conveniently formed during molding by a remov- [it it hardens in chamber 202. When the threaded arrangement is used for grooves 206, it is desirable to provide chamber 202 with means for preventing filler body 204 from threading its way backwardly out of chamber 202 during operation. To this end, axially extending grooves 208 are provided in chamber 202 through grooves 206. As filler body 204 hardens in chamber 202, a portion of it will'extend into grooves 208 to effectively prevent rotation of filler body 204 relative to chamber 202. As is best seen in FIG. 2, grooves 208 are deeper than grooves 206, so that axially extending walls are created which effectively retain the portion of the filler body which is received in grooves 208, but the depth of the grooves may be varied. While one groove 203 would be effective to prevent the unthreading of filler body 204, it is preferable to provide a plurality of axially extending grooves 208 at equally spaced positions around the interior of chamber 202, as is seen in FIG. 3. The rearward end of chamber 202 is chamfered as at'209 to prevent a relatively thin portion of body 204 from being exposed at the rear end of the piston 20.

With further reference to FIG. 2, it has been found that satisfactory axial retention of the filler body is achieved if piston chamber 202 is circumferentially grooved about /3 to /2 of itslength. When grooves 206 are formed by threading, effective retention against unthreading of the filler body has been achieved by providing axial grooves 208 which are about /2 the length of the circumferentially grooved portion. 1

Since sharp angled corners at the bottom and top of grooves are areas of concentrated stress, it is desirable to avoid these in both the piston and the filler body. Therefore, each groove 206 is provided with a rounded bottom portion 207, as is best seen in FIG. 4, rather than a sharp corner as at 210, as would be formed with a normal thread. It will be readily understood that this also efiectively increases the piston wall thickness. It is also desirable to avoid the sharp corners on'the piston wall portions separating the grooves, as at 211, that would be formed by a normal threading operation, since these corners would operate to form a sharp corner at the bottom of the corresponding groove in the filler body. It should be noted that the sharp corner 211 can be eliminated by drilling cavity 202 to a smaller diameter than the diameter of crests of the teeth, and then tapping cavity 202 to form the rounded thread bottom 207 and also the rounded crest able pin. Although the preferred filler material may have a higher coefficient of temperature expansion than the piston itself, the piston walls are made sufiiciently thick to minimize the eifect of thermal expansion on the clearance between piston and cylinder wall.

Novel means are provided'for retaining filler body 204 against axial movement within the piston chamber 202, including a plurality of generally circumferentially extending grooves 206 formed in the inner surface of chamber 202 adjacent the rearward end of piston 20. Each groove 206 is provided with ;a rounded bottom surface 207, as is best seen in FIG. 4, to prevent the creation of a stress riser in the relatively thin wall section of piston body 200. The rounded bottom portion is formed on a radius at least one-third as long as the groove height. Grooves 206 may be formed by tapping the chamber 202 to, in eifect, create a single spirally shaped groove having adjacent convolutions. Alternately, grooves 206 may be formed by providing individual axially spaced grooves in chamber 202. With either groove construction,

it is desirable that the adjacent grooves be positioned closely adjacent to one another, to create relatively numerous gripping surfaces for filler body 204 to engage as at 212 between the threads with the radius of the crest 212 being at least one-third the height of the groove. Alternately, sharp corner 211 may be eliminated by drilling cavity 202 to a sufiiciently large diameter as at 213, and then tapping the cavity to form the rounded groove bottom 207, and thus a generally cylindrical wall 214 is formed on the crest between adjacent threads. The walls of grooves 206 are preferably inclined as at 215 to avoid the creation of surfaces which are disposed at right angles to the piston axis, which would create areas with weak resistance to shearstresses axially of the piston.

For purposes of example, in one operating embodiment, a piston as at 20, which has an outer diameter of about .75 inch with the length of body 201 being approximately 2.5 inches, and with cavity 202 having a diameter of about .5 inch and a length of 2 /3 inches. In the piston the passage 205 through the filler body, and'the passage 203 through the end of the piston each have a diameter of about .1 inch. Chamfer 200 is provided at an angle of 20, for example, with respect to the piston axis. Eighteen threads 206 are provided per inch to a depth of approximately .8 inch in cavity 202, with either crest portion 214 or the alternate crest portion 212 having a diameter of .5 inch. Rounded portion 207 is formed on a radius of about .01 inch, and rounded portion 212 is formed on a radius approximately similar. Grooves 208 are formed with a radius of about .05 inch and extend approximately half the thickness of the cylindrically grooved portion. It should be understood that the above dimensions, which are typical of a satisfactorily operating piston, are given for purposes of example only, and are not intended to limit the invention to the values given.

Referring now to FIG. 5, another form of hydraulic fluid translating device is shown generally at 60, and is of the axial piston type which may be used as a hydraulic pump or motor. The device 60 includes a housing 61 having a cylinder block 62 bolted thereto by a plurality of bolts 64, only one of which is shown, which also pass through an end member 63. A drive shaft 65 extends through housing 61 and through a bore 66 in cylinder block 62, and is supported by bearings 6842. A Wobbler 73 is provided at an appropriate degree of inclination with respect to the axis of drive shaft 65, and is rotatably supported thereon by bearings 74 and 75.

A plurality of cylinders 76 are provided in annular array in cylinder block 62, only one of which is shown in FIG. 5. A piston 77 is reciprocally mounted in each cylinder 76, and includes an axially elongate body 73 having a rounded forward end or nose portion 79. Pistons 77 are generally similar to that shown in FIG. 2, in that they are provided with a hollowed central portion defining a chamber 80 to lighten the weight of the piston. A filler body 81 is provided in chamber 80, and may be formed of the plastic materials mentioned in connection with the piston embodiment illustrated in FIG. 2. Closely spaced circumferentially extending grooves 82 are provided at the rearward end of chamber 80 to retain filler body 81 against axial movement in the chamber 80. A plurality of axially extending grooves are provided through the circumferential grooves 82, only one of which is shown at 83, to prevent filler body 81 from moving in chamber 80 when grooves 82 are formed by threading.

Referring now to FIG. 7, still another form of hydraulic fluid translating device is shown in the form of a radial piston device 90. Device 90 may be used as a pump or motor, as is understood by those in the art, and includes a housing 91 having a hollow interior defining a chamber 92 for reception of the operating parts of the pump mechanrsm.

A rotatable cylinder block 93 is fixed to a suitable drive means 94, and includes a plurality of radially extending cylinders 95. As is known in the art, more than one axially spaced row of cylinders may be provided in cylinder block 93, though in FIG. 7 only one row of cylinders is shown. Pumping pistons 96 are slidable in the cylinders 95, and are urged outwardly by the pressure of the incoming fluid through passages 97, and by centrifugal force as the cylinder block rotates, with the pistons being moved inwardly during rotation of the cylinder block by an eccentric means shown at 98, the eccentricity of which may be adjusted by the means shown generally at 99.

The aforedescribed radial piston pump or motor structure is typified by that shown in the patent to Reinlre, 3,066,613, wherein it is pointed out that the ring 100 of eccentric device 98 is provided with an inwardly concave surface which is engaged by the generally spherically shaped end portion 101 of pistons 96. Piston 96 further includes an axially elongate body portion 102 having a hollowed inner portion defining a chamber 103 that extends generally the entire length of body 102. As described above in connection with pistons and 77, a filler body 104 formed of suitable plastic material is molded in place in chamber 103. Means in the form of generally circumferentially extending and closely spaced grooves 105 are provided to prevent filler body 104 from moving axially within chamber 103, with a plurality of axially extending grooves 106 being cut approximately halfway through grooved portion 105, when grooves 105 are formed by threading, to prevent filler body 104 from moving in chamber 103. Filler body 104 is provided with a generally cylindrically shaped axial extension 107 at the 6 rearward 'end thereof, that is cooperable with ports 97 to assist in expelling fluid from cylinders on the inward stroke of the pistons 96, and to aid in reducing the space occupied by compressible fluid.

I claim:

1. A pistonfor a pump or a motor comprising: a piston body having a hollow interior, at least one generally circumferentially extending groove in the interior of said piston body and having a rounded bottom portion, said rounded bottom portion being formed on a radius at least one-third of the height of said groove, said piston body having rounded portions adjacent the mouth of said groove, and a filler body in said piston body interior and having a portion received in said groove to prevent axial displacement of said filler body relative to said piston.

2. A piston for a pump or a motor comprising: a piston body having a hollow interior, at least one generally circumferentially extending groove in the interior of said piston body and having inclined side walls, and a filler body molded within said piston body interior and having a portion received in said groove to prevent axial displacement of said filler body relative to said piston.

3. A piston for a pump or motor comprising: a piston body having a hollow interior, a generally circumferentially extending spirally shaped groove in the interior of said piston body and having adjacent convolutions spaced relatively closely to one another, and a filler body in said piston body interior having a portion received in said groove to prevent axial displacement of said filler body relative to said piston, said grooved piston portion having means for preventing rotation of said filler body relative to said piston.

4. A piston as defined in claim 3 wherein said last named means includes at least one axially extending groove in said piston grooved portion.

5. A piston as defined in claim 4 wherein said axially extending groove is deeper than said circumferentially extending groove.

6. A piston as defined in claim 4 wherein a plurality of axially extending grooves are provided at equally spaced positions around said piston interior.

7. The pump or motor device including a cylinder block at least one cylinder therein, a piston reciprocally mounted in said cylinder and comprising: a piston body having a hollow interior, a plurality of axially spaced generally circumferentially extending grooves in the interior of said piston body, and a filler body in said piston body interior and having portions engaging each of said axially spaced grooves to prevent axial displacement of said filler body relative to said piston.

8. In a pump or motor device including a cylinder block with at least one cylinder therein, a piston reciprocally mounted in said cylinder and comprising: a piston body having a hollow interior, at least one generally circumferentially extending groove in the interior of said piston body, the bottom portion of said groove being rounded and having a radius at least one-third of the groove height.

9. The piston as defined in claim 8 wherein said piston includes an end portion extending axially from said piston body, and wherein aligned and communicating openings are provided in said filler body and in said end portion.

10. The piston body as defined in claim 8 wherein saidfiller body is formed of a plastic material.

11. A piston for a multiple piston rotary pump comprising: a piston body having a hollow interior forming a cylindrical wall, said body having a circumferentially extending groove on the inner surface of said wall, a filler body within said hollow interior and engaging said inner surface of said wall and having a portion received in said groove to prevent axial displacement of said filler body relative to said piston, the filler body having a higher coefficient of thermal expansion than said piston body, and the cylindrical wall being of suflicient thickness to prevent the expansion of the filler from causing radial expansion of the outer diameter of the piston.

12. A piston for a multiple piston rot-ary pump comprising: a piston body having a hollow interior forming a cylindrical wall, a ci-rcumferentially extending groove in said wall, a filler body molded within said hollow interior and having a portion engaging said groove to prevent axial displacement of said filler body relative to said piston, the filler body having a coefficient of thermal expansion greater than the piston body, and the cylinder wall being of sutficient thickness to prevent the expansion of the filler body-from causing expansion of the outer diameter of the piston body.

13. A piston for a multiple piston rotary pump as defined inclaim 12 wherein said groove has a rounded bottom portion having a radius at least one-third of the groove height.

14. A piston for a multiple piston rotary pump as defined in claim 12 and further including means for preventing rotation of the filler body relative to said piston.

15. A piston for a multiple piston rotary pump as defined in claim 14 wherein said means includes an axially extending groove in said piston body wall intersecting said circumferentially extending groove, and said filler body being molded to conform to said axially extending groove thereby preventing rotation of said filler body within said piston body.

16. A piston for a multiple piston rotary pump as defined in claim 15 wherein said axially extending groove is deeper than said circumferentially extending groove.

17. A multiple piston pump or motor comprising: a port member having control ports therein, a rotatable cylinder block engaging said port member'and having a 'plurality of cylinders therein selectively communicating with said control parts; pistons slidably mounted in said cylinders and including a piston body having a hollow interior forming a. cylindrical wall, said wall having a circumferentially extending groove therein, a filler body molded within said piston body and having a portion engaging said groove, the filler body having a coefiicient of thermal expansion greater than that of the piston body,

and the piston body being of sufficient thickness to pre- 8 tion having a radius at least one-third of the groove height.

19. A multiple piston pump as defined in claim 17, and further including an axial groove in said cylindrical wall, said filler bodybeing molded into said axial groove to thereby prevent rotation of the filler body relative to the piston body.

20. A multiple piston fluid pump or motor comprising: a port member having control slots for transferring fluid, a rotatable cylinder block engaging the port member and having a plurality of cylinders therein; pistons slidably mounted in said cylinder for receiving and expelling fluid through said control slot-s, each of said pistons including a piston body having a hollow interior forming a cylindrical wall, said cylindrical wall having a spiral groove extending from the end of the piston body inwardly approximately one-third the length of said hollow interior, said groove having a rounded bottom portion with a radius at least one-third the groove height, the crests formed by adjacent portions of'the groove being rounded to prevent undesired stresses in said Wall, a plurality of axially extending grooves in said Wall intersecting said spiral groove and extending from said end of the piston body inwardly, said axially extending grooves being deeper than said spiral groove, a phenolic plastic filler molded Within said hollow interior and conforming in shape to said axially extending groove and said spiral groove thereby preventing rotation and axial movement of the filler with respect to the piston body, the plastic filler having a higher coefficient of thermal expansion than said piston body, the piston body being of sufficient thickness to prevent the expansion of the plastic filler from causing any increase in the outer diameter of the piston-body, and an axially extending lubricating passage through said filler and said piston body.

References (Jited by the Examiner UNITED STATES PATENTS 152,541 6/74 Winchester 92-248 X 242,995 6/81 Shortt 92248 X 3,080,854 3/63 Wiggermann 92-469 X FOREIGN PATENTS 390,420 7/08 France.

RICHARD B. WILKINSON, Primary Examiner. KARL J. ALBRECHT, Examiner. 

1. A PISTON FOR A PUMP OR A MOTOR COMPRISING: A PISTON BODY HAVING A HOLLOW INTERIOR, AT LEAST ONE GENERALLY CIRCUMFERENTIAL EXTENDING GROOVE IN THE INTERIOR OF SAID PISTON BODY AND HAVING A ROUNDED BOTTOM PORTION, SAID ROUNDED BOTTOM PORTION BEING FORMED ON A RADIUS AT LEAST ONE-THIRD OF THE HEIGHT OF SAID GROOVE, SAID PISTON BODY HAVING ROUNDED PORTIONS ADJACENT THE MOUTH OF SAID GROOVE, AND A FILLER BODY IN SAID PISTON BODY INTERIOR AND HAVING A PORTION RECEIVED IN SAID GROOVE TO PREVENT AXIAL DISPLACEMENT OF SAID FILLER BODY RELATIVE TO SAID PISTON. 